| Abstract: | Mouse 3T3 and chick embryo cells grown in monolayers have been treated with the non-ionic detergents, NP40 or Triton X-100, to give “nuclear monolayers”. Immunofluorescence microscopy with antibodies against actin shows that most of the microfilament bundles remain detergent resistant and form part of the cell's cytoskeleton. Sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis of cytoskeleton preparations from chick embryo fibroblasts show the following major proteins: the lower molecular weight histones, a protein coelectrophoresing with actin and a protein, X, of molecular weight approx. 58 000 which is different from tubulin. Thus, at least in well spread cells containing a strongly developed system of microfilamentous bundles, the detergent-resistant cytoskeleton includes the nucleus, large amounts of the 58 000 molecular weight protein and the microfilamentous bundles. The importance of the existence of microfilamentous actin in the cytoskeleton is discussed in relation to previous reports on the existence of actin as a major non-histone protein in the nucleus. |
